1. Field of the Invention
The present invention relates to a Planar Inverted F Antenna (PIFA) and, in particular, to an integrated composite design of a PIFA having an embedded or built-in plastic connector on the Radome surface of the PIFA.
2. Description of the Related Art
With the rapid progress in wireless communication technology and the ever-increasing emphasis for its expansion, wireless modems on laptop computers and other handheld radio devices will be a common. feature. The technology employing a short-range radio link to connect devices such as cellular handsets, laptop computers, and other handheld devices has already been demonstrated [Wireless Design On-line Newsletter, Vol. 3, Issue 5, Nov. 22, 1999]. The performance of the antenna placed on devices like handsets and laptop computers is one of the critical parameters for the satisfactory operation of such a radio link. Therefore, the performance characteristics of the antenna utilized on communication devices assume significant importance in the evolving technology of wireless modems.
In the cellular communication industry, there recently has been an increasing emphasis on internal antennas instead of conventional external wire antennas. The concept of an internal antenna stems from the avoidance of a protruding external radiating element by the integration of the antenna into the device itself. Internal antennas have several advantageous features such as being less prone to external damage, a reduction in overall size of the handset with optimization, and ease of portability. The printed circuit board of the communication device serves as the ground plane of the internal antenna. Among the various choices for internal antennas, PIFA appears to have great promise. The PIFA is characterized by many distinguishing properties such as relative light weight, ease of adaptation and integration into the device chassis, moderate range of bandwidth, Omni directional radiation patterns in orthogonal principal planes for vertical polarization, versatility for optimization, and multiple potential approaches for size reduction. The PIFA also finds useful applications in diversity schemes. The sensitivity of the PIFA to both vertical and horizontal polarization is of immense practical importance in mobile cellular/RF data communication applications because of the absence of the fixed antenna orientation as well as the multi-path propagation conditions. The features enumerated above render the PIFA to be a good choice as an internal antenna for mobile cellular/RF data communication applications.
A conventional prior art single band PIFA assembly with an external RF connector is illustrated in FIGS. 5A and 5B. The PIFA 100 shown in FIGS. 5A and 5B consists of a radiating element 101, a ground plane 102, a connector feed pin 104a, and a conductive post or pin 107. A power feed hole 103 is formed in the radiating element 101 which receives the connector feed pin 104a. The connector feed pin 104a serves as a feed path for radio frequency (RF) power to the radiating element 101. The connector feed pin 104a is inserted through the feed hole 103 from the bottom surface of the ground plane 102 and is electrically insulated from the ground plane 102 where the pin passes through the hole in the ground plane 102. The connector feed pin 104a is electrically connected to the radiating element 101 at 105a with solder. The body of the feed connector 104b is electrically connected to the ground plane at 105b with solder. The connector feed pin 104a is electrically insulated from the body of the feed connector 104b. A through hole 106 is formed in radiating element 101 and a conductive post or pin 107 is inserted through the hole 106. The conductive post 107 serves as a short-circuit-between the radiating element 101 and the ground plane 102. The conductive post 107 is electrically connected to the radiating element 101 at 108awith solder. The conductive post 107 is also electrically connected to the ground plane 102 at 108b with solder. The resonant frequency of the PIFA 100 is determined by the length (L) and width (W) of the radiating element 101 and is slightly affected by the locations of the feed pin 104a and the shorting pin 107. The impedance match of the PIFA 100 is achieved by adjusting the diameter of the connector feed pin 104a, by adjusting the diameter of the conductive shorting post 107, and by adjusting the separation distance between the connector feed pin 104a and the conductive shorting post 107.
In the prior art techniques of PIFA design (Murch R. D., et al., U.S. Pat. No. 5,764,190; Korisch I. A., U.S. Pat. No. 5,926,139) the center conductor of the coaxial cable from the RF source is directly connected to the radiating element of the PIFA at the feed point. Further, in these designs, the feed point of the PIFA is drawn away from the shorted edge of the radiating element and is located within the central surface of the radiating element. Therefore, the feed cable from the RF source has to pass through the interior region (between the radiating element and the ground plane) of the PIFA. Such a prior art feeding scheme of the PIFA will prove to be tedious and cumbersome in the final integration process. An alternative scheme of a PIFA design that circumvents such a tedious feed assembly is therefore desirable. From the structural and fabrication point of view, an avoidance of a feed cable extending through the interior region of the PIFA is preferred. One recourse to accomplish the above task is to terminate the feed point of the PIFA with an external RF connector as explained in the description of a conventional PIFA. In most of the PIFA designs having an external RF connector, the cost of the commercial RF connector is in excess of the cost of the PIFA itself. An innovative design concept of a PIFA circumventing the requirement of an external RF connector for its operation is therefore a significant important feature to realize an enhanced cost-effectiveness of the PIFA technology. Keeping in pace with the rapid miniaturization in the size of the mobile voice and RF data communication devices, the future design of internal antenna should be accomplished without necessitating any change in the overall size of the communication device. The system considerations often warrant placement of the internal antenna at different locations on the device chassis with a very small volume earmarked for it. At times, the ground plane of the internal antenna might be in isolation with the chassis of the radio device resulting in a very small ground plane for the antenna. Under such design restrictions, the internal antenna has to exhibit satisfactory gain and bandwidth performance despite the non-availability of a large ground plane. Therefore, the design concept of an internal antenna such as a PIFA with a very small ground plane which overcomes the existing shortcomings of the PIFA feed structure is highly desirable for wireless applications to facilitate the ease of antenna integration, compactness, and adaptation.
The principal objective of this invention is to provide an encapsulated PIFA module which circumvents the requirement of attachment of a separate and an external RF connector to the feed point of the PIFA.
A further objective of this invention is to provide a design of a PIFA configuration which is devoid of an external metal RF connector.
A further objective of this invention is to provide a PIFA having a very small ground plane so that final PIFA module is compact and miniaturized in size.
Still another objective of this invention is to provide a design configuration of the composite assembly of a PIFA, its Radome and a RF connector for feeding the PIFA as an integrated module.
Still another objective of this invention is provide a structural configuration of a PIFA which is devoid of a feed assembly which passes through the interior region of the PIFA.
Yet another objective of this invention is to provide a composite assembly of a PIFA, its Radome, and a built-in connector which is cost effective to fabricate.
Still another objective of this invention is to provide a PIFA module which is easy for final system integration.
These and other objects will be apparent to those skilled in the art.
The instant invention provides a composite structure of a radiator assembly, a Radome, and an RF connector of a PIFA as an integrated single module. The PIFA of this invention overcomes the need of a separate external RF connector for the PIFA. In the preferred embodiment, the connection of the PIFA to the RF source of the system is through a simple, built-in, or embedded plastic connector which is a part of the Radome of the PIFA. A hollow cylindrical structure formed as an outward extension of the Radome serves as the embedded plastic connector of the PIFA. A metal rod attached to the feed conductor of the PIFA which protrudes into the hollow cylindrical structure of the Radome forms the center pin of the embedded plastic connector of the PIFA. A tab attached to the common ground plane which extends into the hollow cylindrical structure of the Radome provides the ground potential of the embedded plastic connector. The concept of dual radiating elements with a common ground plane and a common feed conductor is also disclosed to achieve the satisfactory performance of the PIFA despite a very small ground plane.